An instrument comprising a latching mechanism is known from EP 1 872 729 A1.
In this instrument, a latching element is realized by an arc-shaped lever, which is attached with one end of the arc at the force transmission element and with the other end of the arc attached to the at least one pivotable jaw part. While the location of a connection between the latching element and the transmission element is distal from the location of a connection of the latching element with the at least one pivotable jaw part in the release state, the location of the connection of the latching element with the transmission element is moved in proximal direction by pulling on the transmission element via the at least one operating element. This leads to a pivot of the at least one pivotable jaw part and results in a closing of the jaw parts. The two aforementioned locations connected via the flexible arc-shaped element, i.e. the latching element, are thereby getting closer together, until an end point is reached wherein the location of the connection between arc-shaped element and transmission element lies slightly proximal with respect to the connection location of the arc-shaped element and the pivotable jaw part. In this position, an over-center state is reached, which is possible because of the flexibility of the latching element, i.e. the arc-shaped element. This stable state forms the basis of the latching mechanism.
As the instrument is equipped to accommodate objects of different diameter, the aforementioned latching mechanism has to be formed in that way that even with a small object, e.g. a needle of small diameter, the arc-shaped element has to be flexed at least a little in order to provide a working latching mechanism.
When accommodating larger objects, such as needles comprising a larger diameter, this results in a much higher flexing of the arc-shaped element and, therefore, in a higher strain for the material. This means that due to the higher and often different stress acting on the latching element, a high amount of strain occurs, which may exceed the elastic limit of the construction material resulting in permanent bending damage.
In order to decrease this strain, the aforementioned citation suggests to equip the part of the at least one pivotable jaw part which connects with the latching element with a certain flexibility. However, even here a permanent strain occurs after some time, due to the flexing movements.
Further, due to the limitations given by the material properties and the design of such a small mechanical instrument and mechanism, the needle holding force and the maximum jaw opening angle are both sub-optimal. This is also due to the aforementioned needed capability of this instrument to accommodate small as well as larger objects.
Further, WO 2005/092216 A1 shows an instrument used for surgical laparoscopy. This instrument is designed such that a pivotable jaw part comprises a pin at the opposite end with respect to the cutting part of the jaws. This pin is slidingly received in a groove of an axially moveable element. The groove may comprise an elevation shift at its bottom. In this elevation shift the aforementioned pin may be temporarily received while the pin moves along this groove due to the axial movement of the element. This results in a temporarily lock of the pin without affecting the linear motion of the jaws relative to the handle actuation.
This design comprises only one locked position as well. Also, due to the design with the short pin being slidingly arranged in a groove the locked position is not very stable, especially when stronger forces are applied in order to hold the aforementioned objects, like needles. Also, for the same reasons a twisting of the jaw parts in the direction of the pivot axis may occur due to the strong forces acting on the jaw parts when the aforementioned objects are grasped.
It is therefore an object of the present invention to improve the medical instruments of the kind mentioned before, such that the aforementioned drawbacks are avoided, in particular that the instrument is capable to accommodate objects of different sizes safely with the necessary holding force between the two jaw parts while simultaneously the strain in the parts is eliminated or at least reduced.